I have a question regarding this. As a layman, how would the ability to process milk past infancy affect the evolution of our species? Are there really enough people dying from this trait to have it affect mate selection/child bearing?

Welcome to real life. I have 5 or 6 variations on ways to get to work. I beat some coworkers by as much as 20-25 minutes simply because they refuse to go anyway but the standard way everyone else goes.